Moist turbulent Rayleigh-Benard convection with Neumann and Dirichlet boundary conditions

Turbulent Rayleigh-Benard convection with phase changes in an extended layer between two parallel impermeable planes is studied by means of three-dimensional direct numerical simulations for Rayleigh numbers between 10^4 and 1.5\times 10^7 and for Prandtl number Pr=0.7. Two different sets of boundary conditions of temperature and total water content are compared: imposed constant amplitudes which translate into Dirichlet boundary conditions for the scalar field fluctuations about the quiescent diffusive equilibrium and constant imposed flux boundary conditions that result in Neumann boundary conditions. Moist turbulent convection is in the conditionally unstable regime throughout this study for which unsaturated air parcels are stably and saturated air parcels unstably stratified. A direct comparison of both sets of boundary conditions with the same parameters requires to start the turbulence simulations out of differently saturated equilibrium states. Similar to dry Rayleigh-Benard convection the differences in the turbulent velocity fluctuations, the cloud cover and the convective buoyancy flux decrease across the layer with increasing Rayleigh number. At the highest Rayleigh numbers the system is found in a two-layer regime, a dry cloudless and stably stratified layer with low turbulence level below a fully saturated and cloudy turbulent one which equals classical Rayleigh-Benard convection layer. Both are separated by a strong inversion that gets increasingly narrower for growing Rayleigh number.Comment: 19 pages, 13 Postscript figures, Figures 10,11,12,13, in reduced qualit

Factors affecting the performance of a manufacturing supply chain, and the organization

Abstract: Due to constant failure in delivering the products to customers on time the defence manufacturing organization introduced the supply chain phenomenon into its operations in an attempt to improve its performance (on-time delivery). This research aims to identify if supply chain performance is affected mainly by social or technical factors and also outline which of these factors have the highest effect on the performance of supply chain. The importance of this research is that it will determine if the performance of supply chain is affected by technical or social factors and also how the organization is affected by these factors. This research employed a case study and made use of both qualitative and quantitative data to allow for data triangulation in order to minimize biasness and increase the credibility of the results. The findings indicate that supply chain performance is affected by both social factors and technical factors, however the impact of these factors on both supply chain and the organization is different. In summary, this research will provide insight to the factors that affect the performance of supply chain and accordingly provide methods to minimize or eliminate these factors and therefore reducing their effect on supply chain and the organization

Responding to the challenge of Black Theology: Liberating Ministry to the White Community – 1988–1990

This article provides an initial overview of the Institute for Contextual Theology’s 1988–1990 project on A Liberating Ministry to the White Community, particularly exploring the main themes that emerged from national workshops during the 3 years. The project participants set out to think through the questions of a ministry to the white community in dialogue and in solidarity with Black Consciousness and Black Theology and the article seeks to explore the extent to which this initial focus was attended to in the main themes developed. Particular attention is given to how the project developed the notion of the white church as a ‘site of struggle’ and the accompanying social analysis and understanding of the role of prophetic theology

Phosphoinositide-binding interface proteins involved in shaping cell membranes

The mechanism by which cell and cell membrane shapes are created has long been a subject of great interest. Among the phosphoinositide-binding proteins, a group of proteins that can change the shape of membranes, in addition to the phosphoinositide-binding ability, has been found. These proteins, which contain membrane-deforming domains such as the BAR, EFC/F-BAR, and the IMD/I-BAR domains, led to inward-invaginated tubes or outward protrusions of the membrane, resulting in a variety of membrane shapes. Furthermore, these proteins not only bind to phosphoinositide, but also to the N-WASP/WAVE complex and the actin polymerization machinery, which generates a driving force to shape the membranes

The other side of whiteness : the Dutch Reformed Church and the search for a theology of racial reconciliation in the afterlife of apartheid

CITATION: Van der Riet, L. R. & Van Wyngaard, C. G. J. 2021. The other side of whiteness : the Dutch Reformed Church and the search for a theology of racial reconciliation in the afterlife of apartheid. Stellenbosch Theological Journal, 7(1):1–25, doi:10.17570/stj.2021.v7n1.t2.The original publication is available at https://ojs.reformedjournals.co.zaThis article will provide an overview and analysis of developments in the Dutch Reformed Church’s (DRC) General Synod concerning race, racism, and racial reconciliation from 1986 until 2019. It seeks to extend the multiple accounts of the DRC’s adoption and rejection of apartheid theology by tracing its further attempts at grappling with questions of racism during and after the transition to democracy, into the present. Three primary discourses are explored, namely the search for an inclusive ecclesiology, the commitment to community involvement in the reconstruction of South Africa after apartheid, and the transformation of interpersonal ethics towards greater respect and care for others. Thereafter, the article highlights four territories that remain largely unexplored within the DRC in the past quarter of a century and argues for their future exploration. These trajectories could contribute to a deeper transformation and conversion from the white Christianity historically tied to the DRC.Publisher's versio

Scalar flux profile relationships over the open ocean

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S09, doi:10.1029/2003JC001960.The most commonly used flux-profile relationships are based on Monin-Obukhov (MO) similarity theory. These flux-profile relationships are required in indirect methods such as the bulk aerodynamic, profile, and inertial dissipation methods to estimate the fluxes over the ocean. These relationships are almost exclusively derived from previous field experiments conducted over land. However, the use of overland measurements to infer surface fluxes over the ocean remains questionable, particularly close to the ocean surface where wave-induced forcing can affect the flow. This study investigates the flux profile relationships over the open ocean using measurements made during the 2000 Fluxes, Air-Sea Interaction, and Remote Sensing (FAIRS) and 2001 GasEx experiments. These experiments provide direct measurement of the atmospheric fluxes along with profiles of water vapor and temperature. The specific humidity data are used to determine parameterizations of the dimensionless gradients using functional forms of two commonly used relationships. The best fit to the Businger-Dyer relationship [ Businger, 1988 ] is found using an empirical constant of a q = 13.4 ± 1.7. The best fit to a formulation that has the correct form in the limit of local free convection [e.g., Wyngaard, 1973 ] is found using a q = 29.8 ± 4.6. These values are in good agreement with the consensus values from previous overland experiments and the Coupled Ocean-Atmosphere Response Experiment (COARE) 3.0 bulk algorithm [ Fairall et al., 2003 ]; e.g., the COARE algorithm uses empirical constants of 15 and 34.2 for the Businger-Dyer and convective forms, respectively. Although the flux measurements were made at a single elevation and local similarity scaling is applied, the good agreement implies that MO similarity is valid within the marine atmospheric surface layer above the wave boundary layer.The FAIRS work was supported by the Office of Naval Research grant N00014-00-1-0403 while the GasEx work was supported by the National Science Foundation grant OCE-9986724

Measurement of turbulence spectra using scanning pulsed wind lidars

Turbulent velocity spectra, as measured by a scanning pulsed wind lidar (WindCube), are analyzed. The relationship between ordinary velocity spectra and lidar derived spectra is mathematically very complex, and deployment of the three-dimensional spectral velocity tensor is necessary. The resulting scanning lidar spectra depend on beam angles, line-of-sight averaging, sampling rate, and the full three-dimensional structure of the turbulence being measured, in a convoluted way. The model captures the attenuation and redistribution of the spectral energy at high and low wave numbers very well. The model and measured spectra are in good agreement at two analyzed heights for the u and w components of the velocity field. An interference phenomenon is observed, both in the model and the measurements, when the diameter of the scanning circle divided by the mean wind speed is a multiple of the time between the beam measurements. For the v spectrum, the model and the measurements agree well at both heights, except at very low wave numbers, k1 < 0.005 m?1. In this region, where the spectral tensor model has not been verified, the model overestimates the spectral energy measured by the lidar. The theoretical understanding of the shape of turbulent velocity spectra measured by scanning pulsed wind lidar is given a firm foundation.Aerodynamics, Wind Energy, Flight Performance and PropulsionAerospace Engineerin

Hysteresis phenomenon in turbulent convection

Coherent large-scale circulations of turbulent thermal convection in air have been studied experimentally in a rectangular box heated from below and cooled from above using Particle Image Velocimetry. The hysteresis phenomenon in turbulent convection was found by varying the temperature difference between the bottom and the top walls of the chamber (the Rayleigh number was changed within the range of $10^7 - 10^8$). The hysteresis loop comprises the one-cell and two-cells flow patterns while the aspect ratio is kept constant ($A=2 - 2.23$). We found that the change of the sign of the degree of the anisotropy of turbulence was accompanied by the change of the flow pattern. The developed theory of coherent structures in turbulent convection (Elperin et al. 2002; 2005) is in agreement with the experimental observations. The observed coherent structures are superimposed on a small-scale turbulent convection. The redistribution of the turbulent heat flux plays a crucial role in the formation of coherent large-scale circulations in turbulent convection.Comment: 10 pages, 9 figures, REVTEX4, Experiments in Fluids, 2006, in pres